The present invention relates to an alkali-soluble adhesive agent which is used for temporarily bonding and fixing a substrate such as a wafer or glass substrate to a polishing turn table in processes of fabricating electronic parts for semiconductor integrated circuits, etc. or wafers for solar cells, lens polishing processes, glass polishing processes for making glasses for liquid crystal substrates flat, etc.
Wafers comprising silicon, gallium-arsenide, etc., which are used for the production of electronic parts for semiconductor integrated circuits, etc. or solar cells are fabricated by slicing an ingot comprising a wafer-constituting material to a thin sheet and, then, polishing the thus sliced thin sheet.
For the fabrication of quartz oscillators, lenses, etc. as well as for the glasses required to be flattened, e.g., glasses for liquid crystal substrates, too, cutting and polishing processes are needed. In the processes of polishing such wafers or lenses, rock crystals, glasses, etc., various resins are used as the adhesive agents for fixing the wafers or the lenses, rock crystals, or glasses to a polishing turn table made up of alumina ceramics, etc.
In this case, the wafers or the rock crystals, lenses or glasses are heated and compressed at a temperature of about 110.degree. C. to a turn table, using an adhesive agent. The wafers or the lenses, rock crystals or glasses fixed to the polishing turn table are mirror polished by polishing cloth using a polishing solution. After the completion of polishing, the wafers or the lenses, rock crystals or glasses are cooled down to room temperature or lower, and then released from the turn table by use of a sharp scraper, etc. to remove a portion of the adhesive agent deposited onto the wafers by washing with alkalis or solvents.
Known so far for the adhesive agents used in the processes of polishing lenses, rock crystals, glasses, etc. are glycol phthalate waxes, epoxy waxes, and ketone waxes (JP-A's 61-16477 and 63-27576). After polishing, such adhesive agents are removed by washing with combustible solvents such as a halogen organic solvent, and an aromatic hydrocarbon organic solvent. However, such solvents pose big problems in view of environmental protection; for instance, they cause air pollution and destruction of natural environments. The use of the combustible solvent offers a plant investment problem because it is required to provide explosionproof systems for the purpose of disaster prevention.
To address the fast tempos of cost reductions and technological innovation in the semiconductor industry, high integration-oriented techniques are now under development; for instance, it is required to increase the diameter of silicon wafers from 200 mm.phi. to 300 mm.phi. from the standpoint of cost reductions, decrease the fineness of patterns from 0.25 .mu.m to 0.18 .mu.m from the standpoint of fine patterning, and increase packing densities from 16 Mbits to 64 Mbits from the standpoint of high densities.
Such finer semiconductor devices cause various contamination sources (particles, metal ions, corrosive ions, organic matters, oxide films, etc.) to have a significant influence on the reliability and fabricating yield of semiconductors. Among others, deterioration in device performance due to contamination with metal ions leads to a pn junction leakage problem, and deterioration in device performance due to corrosive ions is of significance as well. For temporal adhesive agents for silicon wafers, too, it is thus required to reduce the contents of metal ions and corrosive ions and thereby have ever higher purity.
Applicant have already filed patent applications (Japanese Patent Application Nos. 11-304154 and 9-286967) for alkali-soluble adhesive agents obtained by adding a mono- or di-valent alcohol to a bisphenol A type epoxy resin, and a novolak type epoxy resin to form a hydroxyl group, and then allowing the resulting product to react with a carboxylic anhydride. However, the former has the demerit of being likely to decrease in softening point although it is excellent in the surface smoothness demanded for a temporal adhesive agent, whereas the latter has the demerit of being likely to increase in softening point and be poor in surface smoothness as well. Thus, there is still growing demand for an alkali-soluble adhesive agent that can be provided in the form of a ever better temporal adhesive agent.
It is thus a primary object of the present invention to provide an alkali-soluble adhesive agent comprising an alkali-soluble resin having a carboxyl group in its molecule and capable of being removed by an alkali aqueous solution without recourse to any organic solvent, which adhesive agent is of an environmental protection-conscious type and improved in adhesion, adhesion strength, coatability, surface smoothness, softening point controllability, melt viscosity controllability and spread controllability.